1. Field of the Invention
The present invention relates to a bus bar module including a plurality of bus bars. Particularly, the present invention relates to a bus bar module including a current sensor.
2. Description of Related Art
An electrically-driven vehicle using a heavy-current uses a bus bar module in a power conversion apparatus for outputting electric power to a drive motor. The power conversion apparatus includes an inverter circuit for converting direct-current power of a battery into three-phase alternating current power. Since the power conversion apparatus of the electrically-driven vehicle uses a heavy-current, a bus bar module is used to transmit a three-phase output of the inverter circuit. The bus bar module for transmitting a three-phase output has three bus bars extending in parallel to each other.
The power conversion apparatus often includes a current sensor to monitor a three-phase output current. Since an output current is transmitted via a bus bar, the current sensor may be attached to the bus bar. A conventional typical current sensor is constituted by a C-shaped magnetic core surrounding a bus bar, and a magnetoelectric transducer placed in a gap of the magnetic core. The magnetic core gathers a magnetic flux generated around the bus bar due to a current flowing through the bus bar. The magnetic flux thus gathered by the magnetic core pass through the magnetoelectric transducer placed in the gap of the magnetic core. The magnetoelectric transducer detects a magnetic flux density of the magnetic flux to pass therethrough. Since a current has a unique relationship with a magnetic flux density, the detected magnetic flux density corresponds to a magnitude of the current flowing through the bus bar.
In recent years, the sensitivity of the magnetoelectric transducer has improved, and a current sensor including only a magnetoelectric transducer without a magnetic core has been developed. Such a current sensor is compact because the magnetic core is not provided therein. However, without the magnetic core, the sensitivity is often insufficient.
In view of this, a technique to increase sensitivity of a current sensor without a magnetic core has been proposed in International Publication WO2013/005459 and Japanese Patent Application Publication No. 2001-74783 (JP 2001-74783 A). The techniques of WO2013/005459 and JP 2001-74783 A are as follows. The techniques of WO2013/005459 and JP 2001-74783 A relate to a current sensor for measuring currents flowing through bus bars placed in parallel like the bus bar module. Each of the bus bars is provided with a crank-shaped folding portion, and a magnetoelectric transducer is placed in the folding portion. The folding portions of the bus bars in parallel to each other are provided at different positions in an extending direction of the bus bars. Accordingly, the magnetoelectric transducers are also placed at the different positions from each other in the extending direction. Since the positions of the magnetoelectric transducers are different in the extending direction of the bus bars, the crank-shaped folding portion of the bus bar does not affect the magnetoelectric transducers placed in the other bus bars. That is, the techniques of WO2013/005459 and JP 2001-74783 A prevent a SN ratio of a magnetoelectric transducer for measuring a magnetic field of a bus bar from decreasing under the influence of a crank-shaped folding portion of its adjacent bus bar.
Further, WO2013/005459 describes that magnetoelectric transducers to be placed in respective bus bars are attached to one substrate. Slits are provided in the substrate, so that the bus bars are put through the slits.
Further, in JP 2001-74783 A, the layout of a bus bar 11 is determined so that a magnetic flux generated from the bus bar 11 adjacent to a target bus bar 10 to be measured by a magnetoelectric transducer is parallel to a magnetic sensing surface of the magnetoelectric transducer. Accordingly, a magnetic flux density generated from the bus bar 11 is hard to penetrate through the magnetic sensing surface of the magnetoelectric transducer. This makes it possible to restrain the influence of the bus bar 11 with respect to the magnetoelectric transducer.